Choosing a Power Supply: Active vs. Passive PSU

When choosing a power supply for your new or upgraded PC build, one important factor to consider is the PSU’s cooling method. Depending on the brand, wattage, and quality level, users may need to choose between an active, semi-passive, or passively cooled power supply. Here’s a brief overview of the differences between these types of PSU cooling methods and the pros and cons of each.

Actively Cooled Power Supply

An actively cooled power supply is the most common type found on the market. It cools itself with a fan that spins whenever the computer is powered on. The size, quality, and noise level of the fan will vary depending on the PSU’s size and price. Some cheaper or older power supplies will spin the fan at a constant rate, while newer or more expensive units allow for the fan to spin at a variable speed depending on the PSU’s load and temperature. Regardless, with an actively cooled PSU, the fan is always spinning when the power is on.

Pros: Ensures good airflow and cooling for the power supply circuitry at all times; allows for higher wattages; constant cooling may allow for greater component longevity.

Cons: An always-on fan means the potential for constant noise; for units with variable fan speeds, noise may be particularly noticeable during speed changes.

Semi-Passively Cooled Power Supply

A semi-passively cooled power supply is similar to an actively cooled unit with a variable speed fan, except that the fan may completely stop under low loads or temperatures instead of just slowing down. These units are designed to be passively cooled under certain circumstances, but they have the ability to switch to active cooling by spinning up the fan when needed.

Pros: No fan noise when usage is below the active cooling threshold; offers a balance between quiet operation for day-to-day usage and active cooling at higher loads for more demanding gaming or productivity tasks.

Cons: Potentially (although not always) more expensive than their actively cooled counterparts since components must be rated for higher operating temperatures when in passive mode; fan noise may still be audible, especially when spinning up from idle or during subsequent speed changes; requires a case with good airflow when in passive mode; higher temperatures may reduce longevity.

Passively Cooled Power Supply

A passively cooled power supply uses no fan at all, instead relying on heatsinks alone to cool the PSU. This, of course, means no fan noise. But it limits the wattage capabilities compared to active and semi-passive PSUs. It may also limit your choice of case and component layout, as you’ll need to ensure that adequate airflow can reach the power supply’s heatsinks.

Pros: No potential for fan noise; available up to 600 watts, which is adequate for many budget and mid-range PC builds.

Cons: Not truly silent, since electrical noise (whine) will still be present to some degree depending on component quality and load; more expensive (often significantly so) than active and semi-passive counterparts, since they must be rated at higher efficiency; requires a case with good airflow.

Active vs. Passive Power Supplies Overall

When comparing active and passive power supplies (including the passive mode of a semi-passive unit), the two largest issues are noise and wattage. If you need a high wattage power supply, passively cooled and some semi-passive PSUs aren’t yet suitable.

Regarding noise, a passive or semi-passive PSU may be your best option, but you’ll need to ensure that your case and component layout can provide adequate airflow to the power supply’s heatsinks. And if you choose an actively cooled power supply that uses quiet fans, the overall noise level will be minimal and likely indistinguishable from your PC’s other components. Further, as mentioned above, electrical noise will still be a factor for all power supplies, including fully passive models. The level, tone, and frequency of this noise will vary depending on component quality, load, and your case, but it may be audible in certain situations.

While nothing can stop egregious “coil whine,” the low, steady hum of an actively cooled power supply can often drown out common levels of this electrical noise. An active PSU may also prevent you from hearing the spin up of a semi-passive PSU fan as it jumps from idle to active modes, and the constant cooling offered by an active PSU may help increase longevity.

In conclusion, a passive or semi-passive power supply can definitely work, especially for builds where noise is a top priority. But you’ll need to budget for a model with high-end components in order to minimize the effect of electrical noise, and ensure that your case and component layout can provide good airflow to the PSU.

For most PC builders, however, an actively cooled power supply with a high quality quiet fan may be the best option. It provides you with the most wattage options, will likely cost less, and will ensure constant airflow over your power supply’s components, which can keep temperatures lower and potentially extend its life.